Nanosheet devices with CMOS epitaxy and method of forming

ABSTRACT

This disclosure relates to a method of forming nanosheet devices including: forming a first and second nanosheet stack on a substrate, the first and the second nanosheet stacks including a plurality of vertically spaced nanosheets disposed on the substrate and separated by a plurality of spacing members, each of the plurality of spacing members including a sacrificial layer and a pair of inner spacers formed on lateral ends of the sacrificial layer; growing a pair of epitaxial regions adjacent to the first and second nanosheet stacks from each of the plurality of nanosheets such that each of the plurality of inner spacers is enveloped by one of the epitaxial regions; covering the first nanosheet stack with a mask; and forming a pair of p-type source/drain regions on the second nanosheet stack, each of the pair of p-type source/drain regions being adjacent to the epitaxial regions on the second nanosheet stack.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/636,725, filed on Jun. 29, 2017, currently pending and herebyincorporated by reference in its entirety.

BACKGROUND Technical Field

The present disclosure relates to integrated circuit design, and moreparticularly to forming epitaxy layers on complementarymetal-oxide-semiconductor (CMOS) nanosheet transistor devices.

Related Art

Field-effect transistors (FETs) typically include doped source/drainregions that are formed in a semiconductor substrate and separated by achannel region. A nanosheet transistor refers to a type of FET thatincludes a plurality of stacked nanosheets extending between a pair ofsource/drain regions, forming a channel. Nanosheet transistors may beknown as “gate-all-around” transistors in part because the gate isstructured to wrap around the channel. In other words, nanosheettransistors may include a gate that wraps around each of the nanosheets.Another type of gate-all-around transistor is a nanowire transistor.Nanowire transistors may be similar to nanosheet transistors, except thechannel may include nanowires instead of nanosheets. Thisgate-all-around structure can provide very small devices with betterswitching control, lower leakage current, faster operations, and loweroutput resistance.

Nanosheet devices may be difficult to manufacture because of the verysmall size of the devices. For example, in very small devices such asnanosheet FETs, small variations in manufacturing may change electricalproperties of the device, and may also decrease reliability andlongevity of the device. In these cases, it may be beneficial to protectcertain components of the device during manufacturing to increase yieldand reliability of the device.

SUMMARY

A first aspect of the disclosure provides a method including: forming afirst and second nanosheet stack on a substrate, the first and thesecond nanosheet stacks each including a plurality of vertically spacednanosheets disposed on the substrate and separated by a plurality ofspacing members, each of the plurality of spacing members including asacrificial layer and a pair of inner spacers formed on lateral ends ofthe sacrificial layer; growing a pair of epitaxial regions adjacent toeach of the first and the second nanosheet stacks from each of theplurality of nanosheets such that each of the plurality of inner spacersis enveloped by one of the epitaxial regions; covering the firstnanosheet stack with a mask; and forming a pair of p-type source/drainregions on the second nanosheet stack, each of the pair of p-typesource/drain regions being adjacent to one of the epitaxial regions onthe second nanosheet stack.

A second aspect of the disclosure provides a semiconductor deviceincluding: a first and second nanosheet stack on a substrate, the firstand the second nanosheet stack being adjacent to each other and eachincluding vertically spaced nanosheets; a pair of semiconductor layersdisposed on the second nanosheet stack in contact with sidewalls of thenanosheets of the second nanosheet stack, each of the pair ofsemiconductor layers extending vertically from a lowermost nanosheet ofthe second nanosheet stack to an uppermost nanosheet of the secondnanosheet stack; a pair of n-type source/drain regions disposed on thesubstrate adjacent to the first nanosheet stack; and a pair of p-typesource/drain regions disposed on the substrate adjacent to the secondnanosheet stack and in direct contact with the pair of semiconductorlayers.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of this disclosure will be described in detail, withreference to the following figures, wherein like designations denotelike elements, and wherein:

FIG. 1 shows a cross sectional view of a plurality of nanosheet stacksin accordance with the present disclosure.

FIG. 2 shows a cross sectional view of recessing the sacrificial layersbetween the nanosheets in accordance with the present disclosure.

FIG. 3 shows a cross sectional view of forming a plurality of innerspacers in accordance with the present disclosure.

FIG. 4 shows a cross sectional view of growing a first epitaxial regionin accordance with the present disclosure.

FIG. 5 shows a cross sectional view of forming a liner over thenanosheet stacks in accordance with the present disclosure.

FIG. 6 shows a cross sectional view of removing a portion of the firstepitaxial region on the second nanosheet stack in accordance with thepresent disclosure.

FIG. 7 shows a cross sectional view of forming p-type source/drainregions on the second nanosheet stack in accordance with the presentdisclosure.

FIG. 8 shows a cross sectional view of removing the liner in accordancewith the present disclosure.

FIG. 9 shows a cross sectional view of forming a second liner inaccordance with the present disclosure.

FIG. 10 shows a cross sectional view of masking the second nanosheetstack in accordance with the present disclosure.

FIG. 11 shows a cross sectional view of removing a portion of the firstepitaxial region on the first nanosheet stack in accordance with thepresent disclosure.

FIG. 12 shows a cross sectional view of forming n-type source/drainregions on the first nanosheet stack in accordance with the presentdisclosure.

FIG. 13 shows a cross sectional view of a first and second nanosheetdevice in accordance with the present disclosure.

FIG. 14 shows a cross sectional view of growing an n-type doped epitaxyon the first and second nanosheet stacks in accordance with analternative embodiment of the present disclosure.

FIG. 15 shows a cross sectional view of forming a liner in accordancewith an alternative embodiment of the present disclosure.

FIG. 16 shows a cross sectional view of masking the first nanosheetstack in accordance with an alternative embodiment of the presentdisclosure.

FIG. 17 shows a cross sectional view of removing the n-type dopedepitaxy from the second nanosheet stack and growing p-type dopedsource/drain regions on the second nanosheet stack in accordance with analternative embodiment of the present disclosure.

FIG. 18 shows a cross sectional view of a first and second nanosheetdevice in accordance with an alternative embodiment of the presentdisclosure.

DETAILED DESCRIPTION

As noted above, nanosheet devices may be difficult to manufacturebecause of the very small size of the devices. For example, in verysmall devices such as nanosheet FETs, small variations in manufacturingmay change electrical properties of the device, and may also decreasereliability and longevity of the device. In these cases, it may bebeneficial to protect certain components of the device duringmanufacturing to increase yield and reliability of the device.

Some methods of forming nanosheet devices may include areplacement-metal-gate (RMG) process to replace an original dummy gatewith a metal gate. An RMG process can be used to prevent damage to thefinal gate metal during manufacturing. Manufacturing nanosheet devicesmay include initially forming a dummy gate on a stack of nanosheets, andsacrificial layers between the nanosheets. The sacrificial layersbetween the nanosheets may include inner spacers formed on lateral endsthereof. Inner spacers may protect the sacrificial layers duringmanufacturing. The dummy gate and sacrificial layers may later bereplaced by a metal gate with a RMG process as described above.

As one particular example, some integrated circuit (IC) designs includePFET devices adjacent to NFET devices. Such IC designs may be known asbimetallic integrated circuits. A NFET is a FET having an n-channel inwhich the current carriers are electrons. A PFET is a FET having ap-channel in which the current carriers are holes. Source/drain regionsof a NFET device may include a different material than source/drainregions of a PFET device. It may be difficult to accurately manufacturevery small adjacent NFET and PFET nanosheet devices.

One example of difficulty in manufacturing such a configuration is inthe process of selectively applying p-type source/drain regions on PFETdevices that are directly adjacent to NFET devices. Such a process maytypically include covering a NFET device and an adjacent PFET devicewith a first mask, selectively removing the first mask to expose thePFET device, forming p-type source/drain regions on the PFET device,removing the remaining first mask, covering the NFET and PFET deviceswith a second mask, selectively removing the second mask to expose theNFET device, and forming n-type source/drain regions on the NFET device.

Each of the above-referenced masks may be typically formed over eachnanosheet stack in contact with lateral ends of the nanosheets andlateral ends of the inner spacers between the nanosheets. Each of thethree above-referenced mask removal steps typically includes an etchprocess. At such a small scale, it may be difficult to perfectly alignsuch an etch process. An etch that removes all of the liner may alsoremove part of the nanosheets and/or the inner spacers between thenanosheets. Removing part of the inner spacers may negatively affect theelectrical characteristics and reliability of the resulting device. Onthe other hand, an etch applied at a distance away from the innerspacers may not remove all of the mask from the nanosheets. In such acase where the nanosheets remain covered or partially covered by themask, it may be difficult to epitaxially grow semiconductor materialfrom the nanosheets in later manufacturing processes. As describedabove, such a typical manufacturing process may include many etchingsteps in proximity of the inner spacers that require perfect alignmentin order to create a device that meets design specifications. It may notbe feasible to include multiple processes that have such a narrowmargins for success.

Embodiments of the present disclosure provide methods for epitaxialsource/drain formation for nanosheet transistor devices that may be usedin integrated circuits (IC). The present disclosure will describe amethod applied to nanosheet devices as an example, but it should beunderstood that the method could also be applied to nanowire devices.

As described above, some nanosheet FETs may include inner spacersbetween nanosheets to stabilize and electrically isolate portions of thenanosheet device. If the inner spacers are damaged or otherwise end upoutside of the design specification, the electrical properties of theresulting nanosheet FET may render the device inoperable or unreliable.For example, if an etch removes a portion of the inner spacer, theelectrical properties of the resulting device may be outside of designspecifications. On the other hand, if an etch is applied farther fromthe inner spacer to ensure that the inner spacer remains intact, thenanosheets may not be sufficiently exposed for later epitaxial growthprocesses. If the nanosheets are not sufficiently exposed, it may bedifficult or impossible to epitaxially grow source/drain regions fromthe nanosheets. It may not be feasible to include multiple processesthat have a narrow margins for success because of an exposed innerspacer.

The present disclosure provides a method of forming epitaxialsource/drain regions on adjacent NFET and PFET nanosheet devices whileprotecting the inner spacers. Protecting the inner spacer may reduce thenumber of manufacturing processes that have a narrow margin for success.Other benefits of the present disclosure may be clear from the detaileddescription.

It is to be understood that the present disclosure will be described interms of a given illustrative architecture having a silicon substrate,however other architectures, structures, substrate materials, andprocess features and steps may be varied within the scope of the presentdisclosure.

It will also be understood that when an element such as a layer, region,or substrate is referred to as being “on” or “over” another element, itmay be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there may are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it maybe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Methods as described herein may be used in the fabrication of IC chips.The resulting integrated circuit chips may be integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present disclosure, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present disclosure. Thus, the phrases “in one embodiment” or “inan embodiment,” as well as any other variations appearing in variousplaces throughout the specification are not necessarily all referring tothe same embodiment.

It is to be appreciated that the use of any of the following “/,”“and/or,” and “at least one of,” for example, in the cases of “A/B,” “Aand/or B” and “at least one of A and B,” is intended to encompass theselection of the first listed option (a) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C,” such phrasing is intended to encompass the firstlisted option (A) only, or the selection of the second listed option (B)only, or the selection of the third listed option (C) only, or theselection of the first and the second listed options (A and B), or theselection of the first and third listed options (A and C) only, or theselection of the second and third listed options (B and C) only, or theselection of all three options (A and B and C). This may be extended, asreadily apparent by one of ordinary skill in the art, for as many itemslisted.

Referring now to the drawings in which like numerals represent the sameor similar elements, FIG. 1 depicts a plurality of preexisting nanosheetdevices 110. Forming preexisting nanosheet devices 110 may includeforming a first nanosheet stack 106 and a second nanosheet stack 108 ona substrate 102. FIG. 1 shows a phantom discontinuity between firstnanosheet stack 106 and second nanosheet stack 108 to make clear thatfirst nanosheet stack 106 and second nanosheet stack 108 may be formedon the same substrate 102, but not necessarily directly adjacent to eachother. In one embodiment, first nanosheet stack 106 may be formeddirectly adjacent to second nanosheet stack 108, however as shown by thephantom section, such a configuration is not required. In oneembodiment, first nanosheet stack 106 may be formed some distance fromsecond nanosheet stack 108 on the same substrate 102. The phantomdiscontinuity between nanosheet stacks 106, 108 carries through each ofthe FIGS. and serves the same purpose throughout. Substrate 102 mayinclude a silicon substrate, a doped silicon substrate, asilicon-on-insulator (SOI) substrate, or other substrate materialwithout departing from the present disclosure. For example, substrate102 may include a semiconducting material including but not limited tosilicon, germanium, silicon germanium, silicon carbide, and thoseconsisting essentially of one or more III-V compound semiconductorshaving a composition defined by the formula AlX1GaX2InX3AsY1PY2NY3SbY4,where X1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions,each greater than or equal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 beingthe total relative mole quantity). Other suitable substrates includeII-VI compound semiconductors having a composition ZnA1CdA2SeB1TeB2,where A1, A2, B1, and B2 are relative proportions each greater than orequal to zero and A1+A2+B1+B2=1 (1 being a total mole quantity). In oneembodiment, substrate 102 may optionally include a dielectric layer 104on a semiconductor substrate layer 114.

Each of the nanosheet stacks 106, 108 may include a plurality ofalternating nanosheets 116 and sacrificial layers 118. In oneembodiment, nanosheet stacks 106, 108 may include at least one nanosheet116 each. In one embodiment, nanosheet stacks 106, 108 may include threenanosheets 116 each. Sacrificial layers 118 may include silicongermanium (SiGe), or other semiconductor materials. In one particularembodiment, sacrificial layers 118 may include SiGe. Nanosheets 116 mayinclude a semiconducting material such as one of the materials listedabove for substrate 102. In one embodiment, nanosheets 116 may includeundoped silicon (Si). A gate 120 may be disposed on each of thenanosheet stacks 106, 108. Gate 120 may include a metal material or asemiconductor material. In one embodiment, gate 120 may be a dummy gateincluding semiconductor material. In one embodiment, gate 120 mayinclude amorphous silicon (a-Si) disposed on a thin silicon dioxide(SiO₂) layer (not shown). In one embodiment, a gate hard mask 122 may beformed over gate 120. Gate hard mask 122 may include a dielectricmaterial such as silicon nitride (SiN).

FIG. 2 shows a process of recessing sacrificial layers 118. As shown, aportion of sacrificial layers may be removed. Sacrificial layers 118 maybe removed by any now known or later developed techniques for removingsacrificial layers 118 selective to nanosheets 116. For example,sacrificial layers 118 may be recessed using hot NH₄OH:H₂O₂:H₂O, or avapor phase HCl etch. In one embodiment, recessing sacrificial layers118 may include removing SiGe sacrificial layers 118 selective toundoped silicon nanosheets 116. As used herein “etching” generallyrefers to the removal of material from a substrate or structures formedon the substrate by wet or dry chemical means. In some instances, it maybe desirable to selectively remove material from certain areas of thesubstrate. In such an instance, a mask may be used to prevent theremoval of material from certain areas of the substrate. There aregenerally two categories of etching, (i) wet etch and (ii) dry etch. Wetetching may be used to selectively dissolve a given material and leaveanother material relatively intact. Wet etching is typically performedwith a solvent, such as an acid. Dry etching may be performed using aplasma which may produce energetic free radicals, or species neutrallycharged, that react or impinge at the surface of the wafer. Neutralparticles may attack the wafer from all angles, and thus, this processis isotropic. Ion milling, or sputter etching, bombards the wafer withenergetic ions of noble gases from a single direction, and thus, thisprocess is highly anisotropic. A reactive-ion etch (RIE) operates underconditions intermediate between sputter etching and plasma etching andmay be used to produce deep, narrow features, such as trenches.

FIG. 3 shows a process of forming a plurality of inner spacers 124.Inner spacers 124 may include a single dielectric layer (shown), such assilicon nitride (SiN), formed between nanosheets 116 on lateral ends ofsacrificial layers 118 (i.e., where material was removed from lateralends of sacrificial layers 118). In one embodiment, inner spacers 124may be bi-layer spacers including a nitride layer disposed on an oxidelayer (not shown). For example, inner spacers 124 may include an innerSiO₂ layer formed on lateral ends of sacrificial layer 118 and an outerSiN layer disposed on the SiO₂ layer. Together, inner spacers 124 andsacrificial layers 118 may form spacing members 118, 124 that are formedbetween and separate each of the plurality of nanosheets 116. Innerspacers 124 may be formed by a spacer pull-down process, atomic layerdeposition (ALD), or any other now known or later developed techniquesfor forming a dielectric layer on lateral ends of sacrificial layers118. In a particular embodiment, inner spacers 124 may be formed by,after recessing sacrificial layers 118, depositing a conformal layer(not shown) of dielectric material by atomic layer deposition, and thenremoving the conformal layer (not shown) except between nanosheets 116.The portion of the conformal layer left between nanosheets 116 may beinner spacers 124.

FIG. 4 shows a process of growing a first epitaxial region 126 adjacentto nanosheet stacks 106, 108. The terms “epitaxial growth and/ordeposition” and “epitaxially formed and/or grown” mean the growth of asemiconductor material on a deposition surface of a semiconductormaterial, in which the semiconductor material being grown may have thesame crystalline characteristics as the semiconductor material of thedeposition surface. In an epitaxial deposition process, the chemicalreactants provided by the source gases are controlled and the systemparameters are set so that the depositing atoms arrive at the depositionsurface of the semiconductor substrate with sufficient energy to movearound on the surface and orient themselves to the crystal arrangementof the atoms of the deposition surface. Therefore, an epitaxialsemiconductor material may have the same crystalline characteristics asthe deposition surface on which it may be formed. For example, anepitaxial semiconductor material deposited on a {100} crystal surfacemay take on a {100} orientation. In some embodiments, epitaxial growthand/or deposition processes may be selective to forming on semiconductorsurfaces, and may not deposit material on dielectric surfaces, such assilicon dioxide or silicon nitride surfaces.

Returning to FIG. 4, first epitaxial region 126 may be epitaxially grownfrom nanosheets 116. Epitaxially growing first epitaxial region 126 mayinclude vapor-phase, liquid-phase, or solid-phase epitaxy, or any othernow known or later developed techniques for growing epitaxial siliconfrom silicon nanosheets. As shown in FIG. 4, first epitaxial region 126may be grown such that it envelopes (i.e., completely surrounds, seals,or covers) inner spacers 124. First epitaxial region 126 may providephysical support for the fragile (i.e., very small and subject to tightmanufacturing tolerances) inner spacers 124 and nanosheets 116. In oneembodiment, first epitaxial region 126 may include undoped silicon (Si).One advantage of forming first epitaxial region 126 from undoped siliconmay be that undoped silicon may not introduce any dopants to thejunction between nanosheets 116 and first epitaxial region 126.

FIG. 5 shows a process of forming a first liner 128 on an exposedsurface 130 (shown in FIG. 4) of nanosheet stacks 106, 108. In oneembodiment, first liner 128 may be formed conformally over exposedsurface 130. In such an embodiment, first liner 128 may be conformallyformed on first epitaxial region 126, and gate hard mask 122. It shouldbe noted that first epitaxial region 126 may prevent first liner 128from being formed on inner spacers 124. One advantage of this embodimentmay be that inner spacers 124 may be protected from the liner depositionshown in FIG. 5 as well as any subsequent deposition and etchingprocesses that might otherwise damage inner spacers 124. In oneembodiment, first liner 128 may include a dielectric material such asSiN (silicon nitride), SiBCN (silicon borocarbonitride), SiOCN (siliconoxycarbonitride), SiCO (silicon oxycarbide), or SiO₂ (silicon dioxide).In one particular embodiment, first liner 128 may include SiN.

FIG. 6 shows the result of processes including masking first nanosheetstack 106, exposing second nanosheet stack 108, and partially removingfirst epitaxial region 126 on second nanosheet stack 108. The result ofthese processes is shown in a single drawing for brevity. In oneembodiment, a soft mask 132 may be deposited on nanosheet stacks 106,108. Soft mask 132 may include an organic planarization layer (OPL) orother suitable soft mask material. Soft mask 132 may be depositeddirectly on first liner 128 covering nanosheet stacks 106, 108. In oneembodiment, soft mask 132 may include a patterning mask such as aphotoresist mask (not shown separately) that may be deposited over theOPL. The photoresist mask may be patterned and etched (i.e.,lithography) to expose second nanosheet stack 108 while first nanosheetstack 106 remains masked, as shown in FIG. 6. The process of exposingsecond nanosheet 108 may include removing soft mask 132 from secondnanosheet stack 108 and removing first liner 128 from first epitaxialregion 126 on second nanosheet stack 108. In one embodiment, first liner128 may be removed with an etch selective to first epitaxial region 126.In one embodiment, first liner 128 may be removed with a timedanisotropic etch such that horizontal portions of first liner 128 areremoved from first epitaxial region 126, but vertical portions of firstliner 128 remain on sidewalls of gate hard mask 122, as shown. FIG. 6also shows the result of a process including partially removing firstepitaxial region 126 on second nanosheet stack 108. First epitaxialregion 126 on second nanosheet stack 108 may be partially removed withan anisotropic etch selective to substrate 102 and vertical portions offirst liner 128 to reduce a width of first epitaxial region 126 onsecond nanosheet stack 108 such that each of the plurality of innerspacers 124 of second nanosheet stack 108 remains enveloped by one firstepitaxial region 126 on the second nanosheet stack 108. In oneembodiment, as shown in FIG. 6, the remaining portion of first liner 128on second nanosheet stack 108 may act as a mask such that inner spacers124 remain enveloped by a portion of first epitaxial region 126.

FIG. 7 shows processes including removing soft mask 132 (soft mask 132shown in FIG. 6) from first nano sheet stack 106 and forming a pair ofp-type source/drain regions 134 on second nanosheet stack 108. In oneembodiment, p-type source/drain regions 134 may be epitaxially growndoped silicon germanium (SiGe), silicon, or silicon-germanium-tin(SiGeSn). In one embodiment, p-type source/drain regions may includep-type dopants such as boron, gallium, or indium. In one particularembodiment, p-type source/drain regions may include boron-doped SiGe.P-type source/drain regions 134 may be epitaxially grown from remainingportions 136 of first epitaxial region 126. One advantage of thisembodiment may be that the remaining portions of first epitaxial region136 envelope and protect inner spacers 124. Another possible advantageof the present embodiment is that it may be quicker and/or easier toreliably grow p-type source/drain regions 134 from the remaining portionof first epitaxial region 136 compared to epitaxially growing p-typesource/drain regions 134 from nanosheets 116 because of the largeruniform surface area of the remaining portion of first epitaxial region136 compared to sidewalls of nanosheets 116.

FIG. 8 shows a process of removing first liner 128 (liner 128 shown inFIG. 7) from nanosheet stacks 106, 108. First liner 128 may be removedby an etch selective to first epitaxial region 126. At this point, firstnanosheet stack 106 may still include the whole first epitaxial region126 that was formed as described above regarding FIG. 4. Secondnanosheet stack 108 may include p-type source drain regions 134 formedon remaining portion of first epitaxial region 136. In one embodiment,remaining portion of first epitaxial region 136 may include a pair ofundoped silicon layers extending vertically from a lowermost one ofnanosheets 116 of second nanosheet stack 108 to an uppermost one ofnanosheets 116 of second nanosheet stack, as shown. In one embodiment,remaining portion of first epitaxial region 136 may connect and extendbetween the outermost portions of nanosheets 116 on second nanosheetstack 108. In one embodiment, remaining portion of first epitaxialregion 136 may be directly between inner spacers 124 and p-type sourcedrain regions 134 on second nanosheet stack 108.

FIG. 9 shows a process of forming second liner 138 on nanosheet stacks106, 108. Second liner may be formed on nanosheet stacks 106, 108similarly to first liner 128 discussed above regarding FIG. 5. Similarto first liner 128, second liner 138 may include a dielectric material.Second liner 138 may include any of the materials listed above for firstliner 128. In one particular embodiment, second liner 138 may includesilicon nitride (SiN). Also, similar to first liner 128, second liner138 may be conformally formed over nanosheet stacks 106, 108 such thatsecond liner is formed on first epitaxial region 126 on first nanosheetstack 106, and on p-type source/drain regions 134 of second nanosheetstack 108.

FIGS. 10 and 11 show processes including masking second nanosheet stack108 and exposing first nanosheet 106. Similarly as discussed aboveregarding FIG. 6, a soft mask 142 may be deposited on nanosheet stacks106, 108. Soft mask 142 may include an organic planarization layer (OPL)or other soft mask material. Soft mask 142 may be deposited directly onsecond liner 138 covering nanosheet stacks 106, 108. In one embodiment,soft mask 142 may include a patterning mask such as a photoresist mask(not shown separately) that may be deposited over the OPL. Thephotoresist mask may be patterned and etched using a now known or laterdeveloped technique, for example lithography, that is capable ofexposing first nanosheet stack 106 while second nanosheet stack 108remains masked, as shown in FIG. 10. The process of exposing firstnanosheet 106 may include removing soft mask 142 on first nanosheetstack 106 and removing second liner 138 from first epitaxial region 126on first nanosheet stack 106. Second liner 138 may be removed with anetch selective to first epitaxial region 126. In one embodiment, secondliner 138 may be removed with a timed anisotropic etch such that secondliner 138 is removed from first epitaxial region 126, but remains onsidewalls of gate hard mask 122, as shown. FIG. 11 shows the result of aprocess including partially removing first epitaxial region 126 on firstnanosheet stack 106. First epitaxial region 126 may be partially removedwith an anisotropic etch selective to substrate 102. In one embodiment,as shown in FIG. 11, the remaining portion of second liner 138 on firstnanosheet stack 106 may act as a mask such that inner spacers 124 remainenveloped by a portion of first epitaxial region 126 (shown in FIG. 11).In one embodiment, a remaining portion 146 of first epitaxial region 126envelopes inner spacers 124.

FIG. 12 shows processes similar as discussed above regarding FIG. 7,including removing soft mask 142 (soft mask 142 shows in FIG. 11) fromsecond nanosheet stack 108 and forming a pair of n-type source/drainregions 144 on first nanosheet stack 106. In one embodiment, n-typesource/drain regions may include epitaxially grown semiconductormaterial such as silicon or silicon carbide. N-type source/drain regions144 may include n-type dopants such as phosphorous, or arsenic. In oneparticular embodiment, n-type source/drain regions 144 may beepitaxially grown phosphorous-doped silicon (Si). N-type source/drainregions 144 may be epitaxially grown from remaining portions 146 offirst epitaxial region 126 (first epitaxial region 126 shown in FIG.10). Similarly as described above regarding FIG. 7, one advantage ofthis embodiment may be that the remaining portions of first epitaxialregion 146 envelope and protect inner spacers 124. Another possibleadvantage of the present embodiment is that it may be quicker and/oreasier to reliably grow n-type source/drain regions 144 from theremaining portion of first epitaxial region 146 compared to epitaxiallygrowing n-type source/drain regions 144 from nanosheets 116 because ofthe larger uniform surface area of the remaining portion of firstepitaxial region 146 compared to sidewalls of nanosheets 116.

FIG. 13 shows a process of removing second liner 138 (second liner 138shown in FIG. 12) from nanosheet stacks 106, 108. Second liner 138 maybe removed similarly as discussed above regarding first liner 128 andFIG. 8, and the detailed processes are not repeated here for brevity.The resulting structure shown in FIG. 13 may include first nanosheetstack 106 and second nanosheet stack 108 formed on substrate 102.Nanosheet stacks 106, 108 may be formed directly adjacent to each otheron the same substrate 102. Nanosheet stacks 106, 108 may includevertically spaced nanosheets 116. A plurality of sacrificial layers 118may be disposed between each nanosheet 116. In one embodiment, pluralityof inner spacers 124 may be disposed between each nanosheet 116 onlateral ends of sacrificial layers 118. In one embodiment, a pair ofvertically extending semiconductor layers 136 (described above as theremaining portion 136 of first epitaxial region 126 on second nanosheetstack 108) may be disposed on second nanosheet stack 108. Semiconductorlayers 136 may envelope and protect inner spacers 124, and may alsoincrease a rate of epitaxial growth of semiconductor source/drainregions 134/144, compared to epitaxially growing source/drain regions134/144 from the sidewalls of nanosheets 116 themselves, as explainedabove. In one embodiment, semiconductor layers 136 may contact eachnanosheet 116 of second nanosheet stack 108, and envelope inner spacers124 of second nanosheet stack 108. P-type source/drain regions 134 maybe disposed on substrate 102 in direct contact with semiconductor layers136. In one embodiment, a pair of vertically extending semiconductorlayers 146 (described above as the remaining portion 146 of firstepitaxial region 126 on first nanosheet stack 106) may be disposed onfirst nanosheet stack 106. In one embodiment, semiconductor layers 146may contact each nanosheet 116 of first nanosheet stack 106, andenvelope inner spacers 124 of first nanosheet stack. N-type source/drainregions 144 may be disposed on substrate 102 in direct contact withsemiconductor layers 146. In one embodiment, n-type source/drain regions144 may be in direct contact with nanosheets 116 of first nanosheetstack 106.

In some embodiments, after formation of n-type source/drain regions 144and p-type source/drain regions 134, nanosheet stacks 106, 108 may bethermally annealed to promote movement of dopants from source/drainregions 144, 134 to respective junctions between nanosheets 116 andrespective vertically extending semiconductor layers 146, 136. In otherwords, after thermally annealing nanosheet stacks 106, 108, verticallyextending semiconductor layers 146, 136 may include the same dopants asrespective source/drain regions 144, 134. (I.e., vertically extendingsemiconductor layers 146 on nanosheet stack 106 having n-typesource/drain regions 144 may include n-type dopants, and verticallyextending semiconductor layers 136 on nanosheet stack 108 having p-typesource/drain regions 134 may include p-type dopants.) In someembodiments, after thermally annealing nanosheet stacks 106, 108,lateral ends of nanosheets 116 may also include the same dopants asrespective source/drain regions 144, 134. In some embodiments, such ananneal may reduce resistance at the junction between nanosheets 116 andrespective vertically extending semiconductor layers 146, 136.

FIG. 14 shows an alternative embodiment of the present disclosure.Starting with first and second nanosheet stack 106, 108 having innerspacers 124 as described above regarding FIG. 3, FIG. 14 shows a processof forming epitaxial regions similar as described above regarding FIG.4. Unlike FIG. 4 however, FIG. 14 shows forming a first epitaxial region226 that may include n-type doped silicon, compared to first epitaxialregion 126 of FIG. 4 that may include undoped silicon. In oneembodiment, first epitaxial region 226 may include n-type source/drainregions 144 on nanosheet stacks 106 that will become NFET devices.Similarly as described above regarding FIG. 4, first epitaxial region226 may be epitaxially grown from nanosheets 116. As shown in FIG. 14,first epitaxial region 226 may be grown such that it envelopes innerspacers 124. First epitaxial region 226 may provide physical support forthe fragile inner spacers 124 and nanosheets 116.

FIG. 15 shows a process of the alternate embodiment beginning at FIG. 14including forming first liner 228 similarly to the forming of firstliner 128 described above regarding FIG. 5. Similarly to first liner128, first liner 228 shown in FIG. 15 may be formed on an exposedsurface 130 of nanosheet stacks 106, 108 (exposed surface 130 ofnanosheet stacks 106, 108 shown in FIG. 14). In one embodiment, firstliner 228 may be formed conformally over exposed surface 130. In such anembodiment, first liner 228 may be conformally formed on first epitaxialregion 226, and gate hard mask 122. It should be noted that firstepitaxial region 226 may prevent first liner 228 from being formed oninner spacers 124. In one embodiment, first liner 228 may include adielectric material. In one particular embodiment, first liner 228 mayinclude silicon nitride (SiN).

FIGS. 16 and 17 show processes of the alternate embodiment beginning atFIG. 14. These processes are similar to the masking and etchingprocesses described above regarding FIGS. 6 and 7, and every detail isnot reiterated here for brevity. One difference shown in the embodimentof FIG. 17 may be that the entire first epitaxial region 226 may beremoved from second nanosheet stack 108. In other words, there may be noremaining portion of first epitaxial region 226 on second nanosheetstack 108, as shown in FIG. 17. In this embodiment, since firstepitaxial region 226 may include n-type doped semiconductor material,first epitaxial region 226 may need to be removed from any nanosheetstack 108 on which p-type source/drain regions 134 will be formed. Inone embodiment, first epitaxial region 226 may be removed with an etchselective to nanosheets 116, inner spacers 124, and substrate 102. FIG.17 shows the process of forming p-type source/drain regions 134 onsecond nanosheet stack 108. In this embodiment, p-type source/drainregions 134 may be formed by epitaxially growing doped SiGe fromnanosheets 116 of second nanosheet stack 108. In one embodiment, p-typesource/drain regions 134 may include boron-doped SiGe.

FIG. 18 shows a process of the alternate embodiment beginning at FIG. 14including removing first liner 228 (first liner 228 shown in FIG. 17)from first nanosheet stack 106. FIG. 18 also shows the resultingstructure formed by the embodiment beginning at FIG. 14. This structuremay be similar to the structure described above in FIG. 13, and everydetail is not reiterated here for brevity. It should be noted that thestructure shown in FIG. 18 may not include the vertical layers ofundoped silicon 136, 146 (shown in FIG. 13) extending between nanosheets116 and enveloping inner spacers 124. In this embodiment, nanosheets 116of the second nanosheet stack 108 may include partial n-type dopingbecause n-type doped first epitaxial region 226 may have been in directcontact with nanosheets 116 of second nanosheet stack 108, as shown inFIG. 14. For example, during previous processes the direct contactbetween nanosheets 116 of second nanosheet stack 108 and first epitaxialregion 226 may have caused n-type dopants from first epitaxial region226 to diffuse into nanosheets 116 of second nanosheet stack 108. Asshould be understood from the above detailed description, the resultingdevice formed from first nanosheet stack may be a NFET transistordevice, and the resulting device formed from the second nanosheet stackmay be a PFET transistor device.

The description of the present disclosure has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the disclosure in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of thedisclosure. The embodiments were chosen and described in order to bestexplain the principles of the disclosure and the practical application,and to enable others of ordinary skill in the art to understand thedisclosure for various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A method comprising: forming a first and secondnanosheet stack on a substrate, the first and the second nanosheetstacks each including a plurality of vertically spaced nanosheetsdisposed on the substrate and separated by a plurality of spacingmembers, each of the plurality of spacing members including asacrificial layer and a pair of inner spacers formed on lateral ends ofthe sacrificial layer; growing a pair of epitaxial regions adjacent toeach of the first and the second nanosheet stacks from each of theplurality of nanosheets such that each of the plurality of inner spacersis enveloped by one of the epitaxial regions; covering the firstnanosheet stack with a mask; and forming a pair of p-type source/drainregions on the second nanosheet stack, each of the pair of p-typesource/drain regions being adjacent to one of the epitaxial regions onthe second nanosheet stack.
 2. The method of claim 1, wherein the pairof epitaxial regions is formed on each of the plurality of nanosheetstacks prior to the covering of the first nanosheet stack with the mask.3. The method of claim 1, further comprising: prior to forming the pairof p-type source/drain regions, partially removing the pair of epitaxialregions on the second nanosheet stack such that each of the plurality ofinner spacers of the second nanosheet stack remains enveloped by aremaining portion of one of the pair of epitaxial regions on the secondnanosheet stack.
 4. The method of claim 1, further comprising: coveringthe second nanosheet stack with a mask; and forming a pair of n-typesource/drain regions on the pair of epitaxial regions on the firstnanosheet stack.
 5. The method of claim 1, wherein the pair of epitaxialregions on each of the first and second nanosheet stacks includesundoped silicon.
 6. The method of claim 1, wherein the first nanosheetstack is formed adjacent to the second nanosheet stack on the substrate.7. The method of claim 3, wherein the covering of the first nanosheetstack includes: forming a liner over the first and the second nanosheetstacks; forming a soft mask over the liner on the first nanosheet stack;and removing a horizontal portion of the liner over the pair ofepitaxial regions on the second nanosheet stack and leaving a verticalportion of the liner on sidewalls of the second nanosheet stack.
 8. Themethod of claim 7, further comprising etching the pair of epitaxialregions on the second nanosheet stack with an anisotropic etch selectiveto the substrate and the vertical portion of the liner to reduce a widthof the pair of epitaxial regions on the second nanosheet stack such thateach of the plurality of inner spacers of the second nanosheet stackremains enveloped by one of the pair of epitaxial regions on the secondnanosheet stack.
 9. The method of claim 7, wherein the pair of epitaxialregions on each of the first nanosheet stack and the second nanosheetstack is an n-type doped material.
 10. The method of claim 9, furthercomprising removing all of the pair of epitaxial regions from the secondnanosheet stack, selective to the nanosheets of the second nanosheetstack, the inner spacers, and the substrate.
 11. A method comprising:forming a first and second nanosheet stack on a substrate such that thefirst nanosheet stack is adjacent to the second nanosheet stack, thefirst and the second nanosheet stacks each including a plurality ofvertically spaced nanosheets disposed on the substrate and separated bya plurality of spacing members, each of the plurality of spacing membersincluding a sacrificial layer and a pair of inner spacers formed onlateral ends of the sacrificial layer; growing a pair of epitaxialregions adjacent to each of the first and the second nanosheet stacksfrom each of the plurality of nanosheets such that each of the pluralityof inner spacers is enveloped by one of the epitaxial regions, the pairof epitaxial regions on each of the first and second nanosheet stacksincludes undoped silicon; covering the first nanosheet stack with afirst mask; forming a pair of p-type source/drain regions on the secondnanosheet stack, each of the pair of p-type source/drain regions beingadjacent to one of the epitaxial regions on the second nanosheet stack;removing the first mask covering the first nanosheet stack after theforming of the pair of p-type source/drain regions on the secondnanosheet stack; covering the second nanosheet stack with a second mask;and forming a pair of n-type source/drain regions on the pair ofepitaxial regions on the first nanosheet stack.
 12. The method of claim11, further comprising: prior to the forming of the pair of n-typesource/drain regions on the first nanosheet stack, partially removingthe pair of epitaxial regions on the first nanosheet stack such thateach of the plurality of inner spacers of the first nanosheet stackremains enveloped by a remaining portion of one of the pair of epitaxialregions on the first nanosheet stack.
 13. The method of claim 12,wherein the covering of the second nanosheet stack includes: forming asecond liner over the first and the second nanosheet stacks; forming asecond soft mask over the second liner on the second nanosheet stack;and removing a horizontal portion of the second liner over the pair ofepitaxial regions on the first nanosheet stack and leaving a verticalportion of the second liner on sidewalls of the first nanosheet stack.14. The method of claim 11, further comprising: prior to the forming ofthe pair of p-type source/drain regions on the second nanosheet stack,partially removing the pair of epitaxial regions on the second nanosheetstack such that each of the plurality of inner spacers of the secondnanosheet stack remains enveloped by a remaining portion of one of thepair of epitaxial regions on the second nano sheet stack.
 15. The methodof claim 14, wherein the covering of the first nanosheet stack includes:forming a first liner over the first and the second nanosheet stacks;forming a first soft mask over the first liner on the first nanosheetstack; and removing a horizontal portion of the first liner over thepair of epitaxial regions on the second nanosheet stack and leaving avertical portion of the first liner on sidewalls of the second nanosheetstack.